Hey leafy.
Well I think it sounds complicated initially but the the way
I see it is "P" puts it in the range, "I" will flatten out the boost drop, and "D",
"D" will flatten out osculation that too much "I" gives.

It's important to know when you increase "I" then "P" will need to be increased
because boost will go up.

Pretty simple though once you start doing it.

Also. Look how good it targets even in 2nd gear burning out
It never gets full boost doing burn outs!